A 62-year-old man with a 40 pack-year smoking history presents with progressive dyspnea on exertion and chronic productive cough for the past 3 years. He is on tiotropium and salbutamol as needed. Spirometry shows FEV₁ 35% predicted with FEV₁/FVC ratio of 0.62. He denies fever, weight loss, or hemoptysis. On examination, he has pursed-lip breathing and barrel chest. His oxygen saturation is 88% on room air. Chest X-ray shows hyperinflation with no focal consolidation. What is the most appropriate next step in his management?